Fumigation



Sept. 27, 1938A. J. M. BAER Er Al.

FUMIGATION Filed Nov. 1e, 19:55

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Patented Sept. 27, 1938 UNITED STATES PATENT oFFicE FUMIGATION New York Application November 1s, 1935ser1a1 No.`5o,4ss

6 Claims.

This invention relates to an improved method of fumigation of organic products such as furs and the like, and more particularly to a method of carrying out vacuum fumigation of organic products with a, mixture of gases, one of which is absorbed to a great extent by the organic material.

In carrying out vacuum fumigation, the use of mixtures of an inert gas such as carbon dioxide with ethylene oxide, or with methyl formate has proved highly satisfactory and of great value. These mixtures ordinarily comprise a large proportion of carbon dioxide and a minor proportion of ethylene oxide or methyl formate. For instance, a, preferred mixture is nine parts of carbon dioxide to one part of ethylene oxide. The ethylene oxide' is the toxic gas, but the carbon dioxide increases its action in certain manners, and at the same time renders it non-explosive. In some instances only one gas may be introduced to the chamber, the residual gas or gases therein constituting another gas or gases of the mixture.

In the customary manner of fumigation, the organic products are placed within a closed chamber or drum which is then evacuated to a high vacuum. When the desired degree of vacuum has been reached the fumigating gases are admitted to the chamber and raise the pressure, normally however a vacuum always being maintained on the articles. It has been found that when this procedure is followed. the mortality to insects and eggs of insects is dependent upon the time of exposure and upon the concentration of the gas. With a denite concentration of the gas, a certain time will be required. By raising the concentration, the time may be shortened, or by lowering the concentration, a longer time will be necessary.

We have now found that much more rapid fumigation may be secured with a given concentration of gas (i. e., a given pressure of gas), pro.- viding the gases from the part'or parts of the chamber farthest from the entrance of the gases are passed over the organic products near the entrance and returned to the parts away from the entrance. `The reason for this is not clear, but it is apparently due to the fact that the ethylene oxide is absorbed by the organic products near the entrance in a much greater degree than the carbon dioxide so that the gases which reach the part or parts of the tank away from the entrance are markedly decient in ethylene oxide. If these gases, deiicient in ethylene oxide, are then passed over the organic products which have absorbed large amounts of the fumigant apparently an equilibrium is established by which some of the absorbed material is given out and is passed along to other parts oi the chamber.

Whatever the lreason may be, the result of removing gas from the far end of the chamber, passing it over'the organic materials near the entrance and returning it to the far parts of the chamber is a decided saving in time or concentration oi gas. For example, with a mixture of nine parts carbon dioxide and one part of ethylene oxide a saving of time of as much as twenty to forty percent has been accomplished by pumphas been accomplished in spite of the fact that.

the chamber was evacuated to as low as 291/2 inches of vacuum priorl to the admission of the gas and although the circulation was such as to produce no turbulence in the gas within the chamber.

The drawing illustrates diagrammatically an apparatus in which the process may be carried out in several manners. The diagram shows a vacuum treating tank I having one or both of its ends 2 pivotally mounted to serve as a door. This tank may be of any desired size orshape, but for normal commercial practice it generally has a capacity of at least one thousand cubic feet. The tank is provided with a manifold 3 having a plurality of inlet pipes .I and supplied with fumigant through the line 5.

A two-stage vacuum pump 6 connects through the lines 1, 8 and 9 with the treating tank and is operated by suitable means which are not shown. The pump preferably has a capacity sumcient to evacuate the chamber I within a few minutes. The discharge end of the pump connects with an oil separator III from which line II connects with an air ventV I2, with line 9. and also with line I3. The line I3 connects with pressure vessel Il and the line I5. Pressure vessel I4 is adapted to withstand a substantially complete vacuum and also pressures up to one hundred pounds super-atmospheric. Suitable heating means may be provided in this vessel, and are indicated in the drawing by steam coil inlet IS and outlet I'I. The vessel Il is large enough to accommodate fumigant suiiicient for one treatment. A supply tank of fumigant is indicated at I8. A plurality of supply tanks may be used if desired. 1

In carrying out the operation an organic product such as furs, tobacco, food products or the like are placed within the tank and the door 2 closed. The tank is then evacuated to a vacuum, say of 29v inches of mercury by means of the pump 6, the air being vented through the line I2. Such valves as are necessary to close the proper lines are, of course, provided and operated in the normal manner. After a suitable vacuum has been reached, say one-half pound absolute pressure, the pump is stopped and the fumigant is admitted to the tank from the vessel I4 through the lines I5 and 5. While the diagram shows only two entrances of the gas to the tank, this is for simplicitys sake and normally a considerable number of inlets are provided to distribute the gas fairly evenly. In spite of a careful distribution in this manner, the utility of the present process remains, which indicates further that the phenomenon is not simply a matter of diffusion of gas.

Fumigant 1s admitted to the chamber until the 20 pressure therein has been raised, say to five pounds absolute. After the desired amount of fumigant has been introduced, the removal of absorbed ethylene oxide (or methyl formate) from organic products near the entrance may be accomplished in several ways. 'Ihe preferred manner is to pump gas through line 'I from the discharge end of the tank I through the pump 6, the oil separator I and back through the lines I5 and 5 into the manifold 3, the remaining lines being closed oi by valves. With a tank containing, for example, oatmeal, evacuated to a vacuum of 291A; inches and then supplied with enough fumigant to raise the pressure to ve pounds absolute with a temperature of approximately '75 F., in a tank having a capacity of approximately 1,788 cubic feet a pumping of 323 cubic feet of gas per minute (at a pressure of ve iounds absolute) reduced the time necessary for complete mortality very substantially. In this test, the gas was admitted to the tank through a plurality of openings and through a distributor which comprises a series of batlies designed to break up the gas into a great number of tiny streams. l

It is generally preferred to commence recirculation immediately upon the introduction of fumigating gas and continue the recirculation during the introduction of the fumigant.

A second method which reduces the time necessaiy for eifective fumigation is .to follow the rst precedure to the point where the fumigating gas has been introduced into the tank and then to re-evacuate the tank to a vacuum, say as great as 29 inches, the fumigant being stored 'in the vessel I4. In carrying out this operation, a single-stage compressor may be supplied between the pump and the vessel I4. This compressor is not shown in the diagram. Where such a compressor is used, a by-pass may be providedfor use when the compressor is not required. In this process when the tank has been evacuated to the desired point the pump is shut off and the cornpressed gas in the accumulator released directly into the manifold and from there into the chamber .I. This complete cycle is preferably carried out in five minutes or less, and it is preferred to repeat it ten minutes after the completion of the first cycle. It is also preferred to commence the rst cycle within ve minutes after the original introduction of the fumigant. The cycle may be repeated as often as desired, but normally two or three cycles are sufficient.

The gas in the accumulator vessel I4 may be tested from time to time to determine the ethylene oxide content thereof, for example, by means of well-known gas indicators. Make-upv gas may be supplied from ethylene oxide tanks or appropriate mixtures of ethylene oxide and carbon dioxide.

A third method for removing absorbed ethylene oxide from the organic products near the entrance points of the gas is to follow vmethod one, but to reverse the flow of the gas every few minutes, say five minutes or thereabouts. Thus, after the gases have been admitted to the tank the line I is closed and the gases are pumped from the tank through the line 5 and into the tank through the line 9. After a few minutes the line 9 is closed and the gases are pumped from the tank through the line 'I and back through the lines I3, I5 and 5.

The term vacumm fumigation as used herein does not necessarily mean that the fumigation is carried out under a vacuum, but simply that under the ordinary course of events a vacuum or its equivalent is used to free the chamber of air.

What we regard as new, and desire to protect by Letters Patent, is:

l. The method of fumigation of organic products characterized by exhausting an enclosed chamber containing objects to be fumgated to an absolute pressure of the order of half an inch of mercury, admitting to the chamber a mixture of a plurality of fumigating gases one of which is preferentially absorbed by an object to be fumigated, the gases being admitted in an amount suflicient to raise the pressure in the chamber to at least as high as the order of five pounds absolute, whereby the residual gas and the fumigating gases become thoroughly mixed, removing fumigating gases from the chamber and returning removed gases to the chamber to pass over organic products nearer to the original entrance of the gases than the point from which the gases were removed. A

2. The method as set forth in claim 1 in which the preferentially absorbed gas is ethylene oxide. 3. The method as set forth in claim 1 in which the preferentially absorbed gas is ethylene oxide and it is present in a minor amount in a major amount of carbon dioxide.

4. The method as set forth in claim 1 in which the direction of movement of the gases is reversed periodically.

5. The method of fumigation of organic products characterized by exhausting an enclosed chamber containing objects to be fumigated to an absolute pressure ofthe order of half an inch of mercury, admitting to the chamber a mixture of a plurality of fumigating gases one of which is preferentially absorbed by an object to be fumigated, the gasesbeing admitted in an amount suiiicient to raise the pressure in the chamber to at least as high as the order of ve pounds absolute, whereby the residual gas and the fumigating gases become thoroughly mixed, and passing gases which in travel to a distance from their entrance have become deficient in the preferentially absorbed gas, over absorbing objects closer to the gas entrance.

6. The method as set forth in claim 1 in which the removal of fumigating gases from the chamber is accomplished by exhaustion to produce a substantially lower pressure therein and their return is accompanied by a substantial rise in pressure therein. l

JOHN M. BAER. EARL P. COLLINS. 

